ALUMINUM ALLOY FIN MATERIAL FOR HEAT EXCHANGERS, AND METHOD OF PRODUCING THE SAME, AND HEAT EXCHANGER

Abstract

A heat exchanger aluminum alloy fin material, comprising Si 0.5 to 1.5 mass %; Fe 0.1 to 1.0 mass %; Mn 0.8 to 2.2 mass %; Zn 0.4 to 2.5 mass %; and further at least one selected from Cu, Ti, Zr, Cr, and V each in 0.02 to 0.3 mass %, with the balance being Al and unavoidable impurities, wherein a metallographic microstructure before braze-heating is such that a density of second phase particles having a circle-equivalent diameter of less than 0.1 m is less than 110.sup.7 particles/mm.sup.2, and that a density of second phase particles having a circle-equivalent diameter of 0.1 m or more is 510.sup.4 particles/mm.sup.2 or more, wherein a tensile strength before braze-heating, TS.sub.B, a tensile strength after braze-heating, TS.sub.A, and a sheet thickness of the fin material, t, satisfy: 0.4(TS.sub.BTS.sub.A)/t2.1, and wherein the sheet thickness is 150 m or less.

Claims

1. An aluminum alloy fin material for heat exchangers, which aluminum alloy fin material is excellent in corrugation formability and mechanical strength after braze-heating, comprising 0.5 to 1.5 mass % of Si; 0.1 to 1.0 mass % of Fe; 0.8 to 2.2 mass % of Mn; and 0.4 to 2.5 mass % of Zn, and further comprising at least one selected from the group consisting of 0.02 to 0.3 mass % of Cu, 0.02 to 0.3 mass % of Ti, 0.02 to 0.3 mass % of Zr, 0.02 to 0.3 mass % of Cr, and 0.02 to 0.3 mass % of V, with the balance being Al and unavoidable impurities, wherein a metallographic microstructure before braze-heating is such that a density of second phase particles having a circle-equivalent diameter of less than 0.1 m is less than 110.sup.7 particles/mm.sup.2, and that a density of second phase particles having a circle-equivalent diameter of 0.1 m or more is 510.sup.4 particles/mm.sup.2 or more, wherein a tensile strength before braze-heating, TS.sub.B (N/mm.sup.2), a tensile strength after braze-heating, TS.sub.A (N/mm.sup.2), and a sheet thickness of the fin material, t (m), satisfy a relationship: 0.4(TS.sub.BTS.sub.A)/t2.1, and wherein the sheet thickness is 150 pm or less.

2. A method of producing an aluminum alloy fin material for heat exchangers, which aluminum alloy fin material is excellent in corrugation formability and mechanical strength after braze-heating, comprising: casting an aluminum alloy raw material comprising: 0.5 to 1.5 mass % of Si; 0.1 to 1.0 mass % of Fe; 0.8 to 2.2 mass % of Mn; and 0.4 to 2.5 mass % of Zn, and further comprising at least one selected from the group consisting of 0.02 to 0.3 mass % of Cu, 0.02 to 0.3 mass % of Ti, 0.02 to 0.3 mass % of Zr, 0.02 to 0.3 mass % of Cr, and 0.02 to 0.3 mass % of V, with the balance being Al and unavoidable impurities, by a twin roll-type continuous casting and rolling method; at least one intermediate annealing, in which a first annealing of the intermediate annealing is carried out in two stages at different retention temperatures, a retention temperature of a second stage is higher than a retention temperature of a first stage, the retention temperature of the first stage is 300 C. to 450 C., the retention temperature of the second stage is 430 C. to 580 C.; and final cold-rolling at a rolling reduction ratio of 20% to 60%, after performing the intermediate annealing; wherein a metallographic microstructure before braze-heating is such that a density of second phase particles having a circle-equivalent diameter of less than 0.1 m is less than 110.sup.7 particles/mm.sup.2, and that a density of second phase particles having a circle-equivalent diameter of 0.1 m or more is 510.sup.4 particles/mm.sup.2 or more, wherein a tensile strength before braze-heating, TS.sub.B (N/mm.sup.2), a tensile strength after braze-heating, TS.sub.A (N/mm.sup.2), and a sheet thickness of the fin material, t (m), satisfy a relationship: 0.4(TS.sub.BTS.sub.A)/t2.1, and wherein the sheet thickness is 150 m or less.

3. The method of producing an aluminum alloy fin material for heat exchangers according to claim 2, wherein a cooling speed from the time point of completion of a retention for annealing of the second stage to 250 C. is set to 50 C./hour or less.

4. An automotive heat exchanger produced by joining via brazing the aluminum alloy fin material for heat exchangers according to claim 1, which aluminum alloy fin material is excellent in corrugation formability and mechanical strength after braze-heating.

Description

BRIEF DESCRIPTION OF DRAWING

[0030] FIG. 1 is a perspective view schematically illustrating a corrugation-formed test material as produced in Examples.

DESCRIPTION OF EMBODIMENTS

(Alloy Composition)

[0031] First, the reasons for adding the alloying elements of the aluminum alloy fin material of the present invention and the ranges of the amounts of addition thereof, will be explained. Hereinafter, regarding the content, the unit percent (%) is percent (%) by mass, unless otherwise specified.

[0032] Si contributes to enhance the mechanical strength through dispersion strengthening by forming AlFeSi-based, AlMnSi-based, and AlFeMnSi-based compounds together with Fe and Mn, or through solid-solution strengthening by being solid solubilized in the matrix.

[0033] The content of Si according to the present invention is 0.50 to 1.5%. If the content of Si is within this range, the effects described above can be obtained. Further, if the content of Si is too large, the solidus temperature (melting point) of the resultant material is lowered, thereby the possibility for melting at the time of brazing may increase, and at the same time, the amount of solid solution in the matrix increases, to lower the thermal conductivity. A more preferred content of Si is 0.80% to 1.4%.

[0034] Fe enhances the high-temperature strength, and has an effect of preventing deformation at the time of braze-heating. When a twin roll-type casting and rolling method is used, the AlFeSi-based, AlFeMn-based, and AlFeMnSi-based compounds that are formed by Fe together with Si and Mn are finely dispersed, and Fe contributes to enhance the mechanical strength through the dispersion strengthening. Further, Fe has an effect of coarsening the grains after brazing by means of the role of suppressing nucleation at the time of brazing, and has an effect of suppressing solder diffusion. The content of Fe according to the present invention is 0.10 to 1.0%. If the content of Fe is too small, the effects above become small, and a high-purity virgin aluminum ingot must be utilized, to cause the costs high. Further, if the content of Fe is too large, huge intermetallic compounds are generated at the time of casting, to lower plastic workability, and to wear the die at the time of corrugation forming. Further, the number of cathode sites is made larger, to increase the number of corrosion starting points, to lower the self-corrosion resistance. A more preferred content of Fe is 0.20 to 0.90%.

[0035] Mn contributes to enhance the mechanical strength through dispersion strengthening by forming AlMnSi-based and AlFeMnSi-based compounds together with Si and Fe, or through solid-solution strengthening by being solid solubilized in the matrix. Further, since Mn has an effect of lower the amount of Si solid solution, melting at the time of brazing can be suppressed by raising the solidus temperature (melting point) of the resultant material. The content of Mn according to the present invention is 0.80 to 2.2%. If the content of Mn is too small, the effects described above are insufficient. Further, if the content of Mn is too large, huge intermetallic compounds are generated at the time of casting, to lower plastic workability, and the solid solution amount in the matrix is made large, thereby for lowering the thermal conductivity. A more preferred content of Mn is 1.0 to 1.6%.

[0036] Zn has an effect of enhancing the sacrificial anode effect (the sacrificial anticorrosive effect), by lowering the natural potential of the resultant fin. The content of Zn according to the present invention is 0.40 to 2.5%. If the content of Zn is too small, the effects described above are small. Further, if the content of Zn is too large, the corrosion speed is made faster, and the self-corrosion resistance of the resultant fin is deteriorated. Furthermore, if the content of Zn is too large, the amount of solid solution of Zn in the matrix is made large, to lower the thermal conductivity. A more preferred content of Zn is 0.50 to 1.5%.

[0037] The fin material of the present invention further contains a predetermined amount(s) of one or more elements selected from Cu, Ti, Zr, Cr, and V.

[0038] Cu contributes to mechanical strength enhancement through solid-solution strengthening by being solid-solubilized in the matrix. The content of Cu according to the present invention is 0.02% to 0.30%. If the content of Cu is too small, the effects are small. Further, if the content of Cu is too large, the amount of solid solution in the matrix becomes large, to lower thermal conductivity. Further, the sacrificial anticorrosive effect is lowered by increasing the spontaneous potential of the fin (making the spontaneous potential of the fin noble). A more preferred content of Cu is 0.10 to 0.20%.

[0039] Ti, Zr, Cr, and V all have an effect of enhancing mechanical strength. The contents of Ti, Zr, Cr and V are each 0.02% to 0.30%. If the contents of Ti, Zr, Cr and V are too small, the effects described above are small. Further, if the contents of Ti, Zr, Cr and V are too large, huge intermetallic compounds are generated at the time of casting, to lower plastic workability, and also, since the amount of solid solution in the matrix becomes large, thermal conductivity is lowered.

[0040] Further, regarding the balance of aluminum and the unavoidable impurities contained in the fin material of the present invention, the respective contents of the unavoidable impurities are preferably 0.05% or less, and the total amount is preferably 0.15% or less.

(Metallographic Microstructure Before Braze-Heating)

[0041] The metallographic microstructure before braze-heating of the aluminum alloy fin material of the present invention will be explained.

[0042] Fine second phase particles (for example, AlMn, AlMnSi, AlFeSi, and AlFeMnSi-based compounds) having a circle-equivalent diameter of less than 0.1 m, have an effect of suppressing nucleation of recrystallization, upon the recrystallization of the fin at the time of braze-heating. Thus, if the density of those second phase particles is too high, a fiber microstructure may remain in a metallographic microstructure before braze-heating, and the recrystallization does not easily occur. Then, the recrystallization is not completed before the solder melts, the solder penetrates into the fin, and thereby erosion occurs. In order to suppress such an erosion, it is effective to enhance the driving force for the recrystallization of the fin at the time of braze-heating. In order to do so, raising the final cold-rolling reduction ratio at the time of fin material production can be mentioned as a countermeasure. However, when the final cold-rolling reduction ratio is raised, the strain amount introduced into the material is made large, to enhance the mechanical strength before braze-heating, thereby for deteriorating the corrugation formability.

[0043] In the present invention, the density of the second phase particles having a circle-equivalent diameter of less than 0.1 m is made to set to less than 110.sup.7 particles/mm.sup.2. A more preferred density is less than 510.sup.6 particles/mm.sup.2. The lower limit is not particularly limited, but is generally 110.sup.5 particles/mm.sup.2.

[0044] Second phase particles (for example, AlMn, AlMnSi, AlFeSi, and AlFeMnSi-based compounds) having a circle-equivalent diameter of 0.1 m or more, have a relatively large size, and thus those second phase particles are solid solubilized at the time of braze-heating and are not easily lost. Thus, since the second phase particles remain in the fin even after braze-heating, dispersion strengthening has an effect of enhancing the fin strength after braze-heating. Thus, in the present invention, the density of the second phase particles having a circle-equivalent diameter of 0.1 m or more is 510.sup.4 particles/mm.sup.2 or more. A more preferred density thereof is 110.sup.5 particles/mm.sup.2 or more. The density of the second phase particles having a circle-equivalent diameter of 0.1 m or more is preferably 110.sup.5 particles/mm.sup.2 or more but 110.sup.7 particles/mm.sup.2 or less.

[0045] The density of the second phase particles having a circle-equivalent diameter of less than 0.1 pm can be investigated by making a transmission electron microscopy (TEM) observation of the fin material. The film thickness of an observed area can be measured from equal-thickness fringes, and TEM observation can be made only at sites where the film thickness would be 0.1 to 0.3 m. Further, the density of the second phase particles having a circle-equivalent diameter of 0.1 m or more can be investigated by making a SEM observation of a fin material cross-section. The density of the second phase particles before braze-heating can be determined by subjecting the TEM and SEM photographs to an image analysis.

[0046] In the present invention, it is preferable that the microstructure before braze-heating is composed of a recrystallized microstructure, and that the grain size is 1,000 m or less. In the case where the recrystallization is not achieved by the intermediate annealing, and where a fiber microstructure remains as described above, the mechanical strength of the fin material before heating becomes high, and the corrugation formability is deteriorated. Also, the grain size of the recrystallized grains formed by the intermediate annealing is preferably 1,000 m or less. When the grain size is more than 1,000 m, in the case where grain boundaries exist in the vicinity of the apexes of fin ridges formed when corrugation forming is performed, the fin is bent at the grain boundaries, and the fluctuation in the ridge height of the fin that is finally obtained is made large. Further, in the production of the fin material, as flatness of the material is deteriorated, rolling property is inhibited, and the product quality and productivity of the fin material are deteriorated. A more preferred grain size is 500 m or less.

(Tensile Strength and Sheet Thickness)

[0047] The relationship among the tensile strength before braze-heating, TS.sub.B (N/mm.sup.2), of the fin material of the present invention, the tensile strength after braze-heating, TS.sub.A (N/mm.sup.2), and the sheet thickness of the fin material, t (m), will be explained.

[0048] When a fin material is corrugated into a waveform fin having a predetermined R value, the strain amount at the formed fin ridges is determined by the R value and the sheet thickness of the fin material at the time of waveform forming. The strain distribution in the fin sheet thickness direction is such that the strain in the outermost layer is large, and the strain lowers toward the center of the sheet thickness. Thus, the vicinity of the surface layer is subjected to plastic deformation, and the vicinity of the sheet thickness center is subjected to elastic deformation. When the proportion of this plastic deformation region is small, the formed shape cannot be frozen, and the formed fin ridges spring back, so that a predetermined shape is not obtained.

[0049] When the R value of the fin ridges is constant, as the sheet thickness of the fin material becomes thinner, the strain amount of the outermost layer of the fin ridges lowers. Thus, if the mechanical strength of the fin material before braze-heating is high, the proportion of the plastic deformation region in the fin sheet thickness direction becomes smaller. Thus, in order to perform satisfactory corrugation forming, if the fin material sheet thickness is small, it is necessary to lower the mechanical strength of the fin material before braze-heating.

[0050] On the other hand, if the difference in mechanical strength (TS.sub.BTS.sub.A) of the mechanical strength after braze-heating, that is, mechanical strength in the O-material state, which is a state completed in recrystallization perfectly, and the mechanical strength before braze-heating is too small, the strain amount introduced to the fin material before braze-heating become lowered. If the strain amount in the raw material state is small, the driving force of recrystallization at the time of braze-heating become small, and the recrystallization temperature rises to a high temperature, or recrystallization is not sufficiently completed, and erosion occurs due to molten solder.

[0051] Thus, in the present invention, it is preferable that the tensile strength before braze-heating, TS.sub.B (N/mm.sup.2), the tensile strength after braze-heating, TS.sub.A(N/mm.sup.2), and the sheet thickness of the fin material, t (m), satisfy the following relationship:

0.4(TS.sub.BTS.sub.A)/t2.1Formula 1

[0052] In order to satisfy the relationship of formula 1, the alloy composition of the alloy material may be set as described above. Further, as explained above, for the alloy material before braze-heating, when the metallographic microstructure has a recrystallized structure, the grain size is adjusted to 1,000 m or less, and strain is generated by a predetermined cold-rolling reduction ratio, a fin material having satisfactory formability and brazing property can be obtained. In order to suppress erosion of the fin at the time of brazing, whether there is more than the necessary amount of strain may present in the fin after performing corrugation forming is important. The strain amount of the fin after corrugation forming is the sum of the strain amount of the alloy material, (TS.sub.BTS.sub.A), and the strain amount introduced at the time of corrugation forming. It was found that since the surface layer strain amount of a corrugation formed fin becomes small as the sheet thickness t becomes smaller, the value of (TS.sub.BTS.sub.A)/t serves as an important indicator for the suppression of erosion.

[0053] In the present invention, when the retention temperature of the intermediate annealing (the annealing temperature) is set in at least two stages, the latter stage is performed at a higher temperature than the former stage, and thereby the density of the second phase particles having a particle size of 0.1 m or more becomes larger, the mechanical strength after the braze-heating can be prevented from being too low. By performing annealing in two stages as such, even if the value of (TS.sub.BTS.sub.A) is small, erosion of the fin does not occur, and a fin material having satisfactory corrugation formability can be obtained. Also, a fin material which satisfies the formula 1 in connection with the mechanical strengths before braze-heating and after braze-heating can be prepared.

[0054] If (TS.sub.BTS.sub.A)/t is smaller than 0.4, the driving force of recrystallization at the time of braze-heating is small, to occur erosion. If (TS.sub.BTS.sub.A)/t is larger than 2.1, when corrugation forming is performed, the proportion of the plastic deformation region in the sheet thickness direction of the fin ridges becomes small, springback occurs, and the corrugation forming property is deteriorated. A more preferred range of (TS.sub.BTS.sub.A)/t is 0.5 to 2.0.

[0055] The sheet thickness of the aluminum alloy fin material for a heat exchanger of the present invention is 150 m or less, preferably 40 to 100 m, and more preferably 40 to 80 m. In the present invention, the aluminum alloy fin material has a feature that the fin material can be made particularly thin.

(Production Method of the Fin Material)

[0056] Next, the production method of the present invention of the aluminum alloy fin material will be described.

[0057] First, an aluminum alloy having the alloy composition described above is melted, and a sheet-shaped ingot is produced by a twin roll-type continuous casting and rolling method. A twin roll-type continuous casting and rolling method is a method of: supplying molten aluminum metal between a pair of water-cooled rolls through a molten-metal supplying nozzle made of a refractory material; and continuously casting and rolling a thin sheet, and examples include a Hunter's method and a 3C method.

[0058] In a twin roll-type continuous casting and rolling method, the cooling speed at the time of casting is larger by several times to several hundred times than that of a DC (Direct Chill) casting method or a twin belt-type continuous casting method. For example, while the cooling speed in the case of a DC casting method is 0.5 to 20 C./sec., the cooling speed in the case of the twin roll-type continuous casting and rolling method is 100 to 1,000 C./sec. Accordingly, the twin roll-type method has a feature that crystallization products, for example, of AlFeSi-based, AlFeMn-based, and AlFeMnSi-based compounds produced at the time of casting, are dispersed more finely and more densely, as compared to the DC casting method or the twin belt-type continuous casting and rolling method. These crystallization products dispersed at a high density accelerate precipitation of elements that are solid-solubilized in the matrix, such as Mn and Si, and thereby contribute to the enhancement of mechanical strength and thermal conductivity. Also, the twin roll-type method is advantageous in that almost no coarse crystallization products having a size in the order of several micrometers (m) are produced, which wear down the die when the fin material is worked by corrugation forming.

[0059] The molten metal temperature employed when casting is carried out by a twin roll-type continuous casting and rolling method is preferably in the range of 680 C. to 800 C. The molten metal temperature is the temperature of the head box that is disposed immediately before the molten metal supplying nozzle. If the molten metal temperature is too low, coarse intermetallic compounds are produced inside the molten metal supplying nozzle, and when those are mixed into the sheet-shaped ingot, the intermetallic compounds cause sheet cracking at the time of cold-rolling. If the molten metal temperature is too high, aluminum is not sufficiently solidified between the rolls at the time of casting, and a normal sheet-shaped ingot cannot be obtained. A more preferred molten metal temperature is 700 C. to 750 C.

[0060] Then, the sheet-shaped ingot thus obtained is subjected to at least one steps of intermediate annealing in the mid course of rolling the ingot to the final sheet thickness. A first intermediate annealing among the intermediate annealing steps carried out one or more times is carried out in two stages with different retention temperatures, under the conditions that the retention temperature of the second stage is higher than the retention temperature of the first stage. The temperature difference is preferably 80 C. to 150 C.

[0061] When the fin material is subjected to annealing, the dispersed state of second phase particles that are precipitated in the fin material changes due to the operation temperature. When annealing is performed at a low temperature, precipitation of finely and densely dispersed second phase particles occurs in the fin material, and when annealing is performed at a high temperature, precipitation of coarsely and sparsely dispersed second phase particles occurs in the fin material. Thus, when annealing is performed at a low temperature, a large number of fine second phase particles that inhibit recrystallization at the time of braze-heating are precipitated out, and erosion of the fin is apt to occur. When annealing is performed at a high temperature, fine second phase particles that inhibit recrystallization at the time of braze-heating are hardly precipitated out, but the dispersion density of the second phase particles is become low, and the mechanical strength after braze-heating is lowered.

[0062] Thus, in the intermediate annealing in the present invention, is conducted to be retained at two stages of temperatures. First, a large number of fine second phase particles are precipitated out in the fin material, upon the retention at a low temperature of the first stage. Then, the fine second phase particles precipitated in the first stage are coarsened, upon the retention at a high temperature of the second stage, the density of fine second phase particles having a particle size of less than 0.1 m that inhibit recrystallization is lowered, and the density of second phase particles having a particle size of 0.1 m or more is raised, thereby for being possible to obtain a metallographic microstructure that does not undergo lowering in mechanical strength after braze-heating.

[0063] The retention temperature of the first stage is set to the range of 300 C. to 450 C. If the retention temperature is too low, precipitation of second phase particles upon annealing hardly occurs. If the retention temperature is too high, second phase particles that are already coarsened upon the first stage are sparsely precipitated out, and the mechanical strength after braze-heating is lowered. A more preferred temperature is in the range of 350 C. to 430 C.

[0064] The retention temperature of the second stage is a temperature that is higher than that of the first stage, and is set to the range of 430 C. to 580 C. If the retention temperature is too low, coarsening of the second phase particles that have been precipitated upon the first-stage annealing does not occur, and a large number of second phase particles that inhibit recrystallization are dispersed, to cause erosion. If the retention temperature is too high, the second phase particles precipitated out upon the first stage are solid-solubilized again, and the distribution of the second phase particles finally obtained becomes a coarse and sparse distribution, thereby for lowering the mechanical strength after braze-heating. A more preferred temperature is in the range of 450 C. to 550 C.

[0065] The retention times for the first stage and the second stage each are preferably 1 to 10 hours. If the retention time is too short, a desired metallographic microstructure cannot be obtained, and if the retention time is too long, the effect reaches saturation, and thus it is not preferable from the viewpoint of productivity. A more preferred retention time is 2 to 5 hours.

[0066] In the case of performing the annealing after the second annealing or later, the conditions are not particularly limited, but it is preferable to perform the annealing at a temperature higher than or equal to the recrystallization temperature of the aluminum alloy utilized as the fin material. The annealing temperature is preferably 300 C. to 500 C., and the retention time is preferably 1 to 5 hours. More preferred conditions are: an annealing temperature of 350 C. to 450 C.; and a retention time of 1 to 3 hours.

[0067] After completion of the first intermediate annealing, at least one cold rolling is carried out. The annealing is performed appropriately, and then cold rolling to a final sheet thickness of 150 m or less is performed. The final cold-rolling reduction ratio, which is the total rolling reduction ratio when rolling is performed to obtain the final sheet thickness after performing the final intermediate annealing, is set to 20% to 60%. If the final cold-rolling reduction ratio is too low, the driving force of recrystallization at the time of braze-heating is insufficient, recrystallization does not occur sufficiently, and erosion occurs. If the final cold-rolling reduction ratio is too high, the amount of strain introduced by rolling is so large that the mechanical strength of the fin material before braze-heating is made high, and the corrugation forming property is deteriorated. A more preferred final cold-rolling reduction ratio is 25% to 50%.

[0068] In order to control the final cold-rolling reduction ratio, at least one or more intermediate annealing is needed, but in the case of performing intermediate annealing only once, the total cold-rolling reduction ratio to obtain from the sheet thickness after casting to the sheet thickness for performing intermediate annealing is made very high. As such, when the cold-rolling reduction ratio is high, the material becomes hard due to rolling, and thereby cracking may occur in the coil edge portions. If the degree of cracking is large, there is a risk that sheet cracking may occur upon rolling. In order to suppress sheet cracking, it is effective to add a trimming step or an intermediate annealing step, in the mid course of the cold-rolling step, to make the material soft. In the case of performing intermediate annealing for the purpose of suppressing edge cracking, for example, a process may be adopted, which process has: performing the first intermediate annealing at the state where the sheet thickness is relatively thick; performing cold-rolling; performing second intermediate annealing intended for controlling the final cold-rolling reduction ratio; and then rolling the sheet to the final sheet thickness by cold rolling.

[0069] The cooling speed to 250 C. after completion of the second-stage retention in the first annealing is set to 50 C./hour or less. When casting is performed by a twin roll-type continuous casting and rolling method, since the cooling speed at the time of casting is very large compared to the cooling speed of the DC casting method or the twin belt-type continuous casting and rolling method, the solid solubility of Mn or Si after casting is high. Since the initial solid solubility is high as such, the solid solubility of Mn or Si in the fin material after annealing changes largely depending on the cooling speed. When the cooling speed is set to 50 C./hour or less, the second phase particles formed by the second stage annealing grow further, and thereby the solid solubility of Mn or Si can be lowered. If the cooling speed is too high, the solid solubility of Mn or Si of the fin material after annealing is made high, and fine second phase particles that inhibit recrystallization as a result of solid-solubilized Mn or Si finely precipitating out in the later step, are precipitated out, to cause erosion. A more preferred cooling speed after annealing is 40 C./hour or less. The lower limit of the cooling speed is not particularly limited, but the cooling speed is about 10 C./hour, in view of industrial implementation.

(Method of Producing Heat Exchanger)

[0070] The aluminum alloy fin material of the present invention is preferable for an automotive heat exchanger. An automotive heat exchanger can be produced by a usual manner. An outline of the embodiment will be described below.

[0071] A heat exchanger is produced: by combining corrugation worked fins with flat tubes that have been forming worked by roll forming or electric welding; assembling the combination with members, such as plates or tanks; and then heating the assembly to a temperature of about 600 C. according to a brazing method, to integrally join.

[0072] Examples of the brazing method include: a flux brazing method using a non-corrosive flux; and a vacuum brazing method of performing brazing in a vacuum without using any flux.

[0073] In the case of a flux brazing process, a flux is applied on an assembled heat exchanger, and then brazing is performed.

[0074] The details of the production method, reference can be made to paragraph [0002] of JP-A-8-134574, paragraph [0002] of JP-A-7-090443, and the like.

EXAMPLES

[0075] The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited thereto.

[0076] First, aluminum alloys having the alloy compositions indicated in Table 1 were respectively produced by the production method shown in Table 2. In regard to the alloy compositions of Table 1, the symbol - indicates that the value is below the detection limit, and the term balance includes unavoidable impurities.

[0077] For a test material cast by the twin roll-type continuous casting and rolling method, a sheet-shaped ingot thus obtained was cold rolled, and subjected to intermediate annealing in a batch-type annealing furnace for a predetermined sheet thickness, followed by cold rolling to the final sheet thickness, to produce a fin material (tempering: H1n).

[0078] For a test material cast by the DC casting method, the thus-produced ingot was heated to 500 C. without performing any homogenization treatment, and then the ingot was rolled to a desired thickness by hot rolling, to produce a sheet material. Then, the sheet material thus obtained was cold rolled, subjected to intermediate annealing in a batch-type annealing furnace for a predetermined sheet thickness, and cold rolled to the final sheet thickness, to produce a fin material (tempering: H1n).

TABLE-US-00001 TABLE 1 Alloy composition (mass %) Alloy No. Si Fe Mn Zn Cu Ti Zr Cr V Al Example 1 0.5 0.5 1.2 1.5 0.1 Balance according to 2 1.0 0.5 1.2 1.5 0.1 Balance this invention 3 1.5 0.5 1.2 1.5 0.1 Balance 4 1.0 0.1 1.2 1.5 0.1 Balance 5 1.0 1.0 1.2 1.5 0.1 Balance 6 1.0 0.2 0.8 1.5 0.1 Balance 7 1.0 0.2 2.2 1.5 0.1 Balance 8 1.0 0.5 1.2 0.4 0.1 Balance 9 1.0 0.5 1.2 1.0 0.1 Balance 10 1.0 0.5 1.2 2.5 0.1 Balance 11 1.0 0.5 1.2 1.5 0.02 Balance 12 1.0 0.5 1.2 1.5 0.15 Balance 13 1.0 0.5 1.2 1.5 0.3 Balance 14 1.0 0.5 1.2 1.5 0.02 Balance 15 1.0 0.5 1.2 1.5 0.15 Balance 16 1.0 0.5 1.2 1.5 0.3 Balance 17 1.0 0.5 1.2 1.5 0.02 Balance 18 1.0 0.5 1.2 1.5 0.15 Balance 19 1.0 0.5 1.2 1.5 0.3 Balance 20 1.0 0.5 1.2 1.5 0.02 Balance 21 1.0 0.5 1.2 1.5 0.15 Balance 22 1.0 0.5 1.2 1.5 0.3 Balance 23 1.0 0.5 1.2 1.5 0.02 Balance 24 1.0 0.5 1.2 1.5 0.15 Balance 25 1.0 0.5 1.2 1.5 0.3 Balance Comparative 26 0.3 0.5 1.2 1.5 0.1 Balance example 27 1.7 0.5 1.2 1.5 0.1 Balance 28 1.0 0.05 1.2 1.5 0.1 Balance 29 1.0 1.2 1.2 1.5 0.1 Balance 30 1.0 0.2 0.6 1.5 0.1 Balance 31 1.0 0.2 2.4 1.5 0.1 Balance 32 1.0 0.5 1.2 0.2 0.1 Balance 33 1.0 0.5 1.2 2.7 0.1 Balance 34 1.0 0.5 1.2 1.5 0.4 Balance 35 1.0 0.5 1.2 1.5 0.4 Balance 36 1.0 0.5 1.2 1.5 0.4 Balance 37 1.0 0.5 1.2 1.5 0.4 Balance 38 1.0 0.5 1.2 1.5 0.4 Balance

TABLE-US-00002 TABLE 2 Final 1-st intermediate cold-rolling Production annealing 2-nd intermediate reduction process Casting Anneal conditions Cooling speed annealing ratio No method 1-st stage 2-nd stage ( C./h) Anneal conditions (%) Example 1 Twin rolls 300 C. 2 h 530 C. 2 h 30 370 C. 2 h 35 according to 2 Twin rolls 370 C. 2 h 530 C. 2 h 30 370 C. 2 h 35 this invention 3 Twin rolls 450 C. 2 h 530 C. 2 h 30 370 C. 2 h 35 4 Twin rolls 350 C. 2 h 430 C. 2 h 30 370 C. 2 h 35 5 Twin rolls 370 C. 2 h 580 C. 2 h 30 370 C. 2 h 35 6 Twin rolls 370 C. 2 h 530 C. 2 h 20 370 C. 2 h 35 7 Twin rolls 370 C. 2 h 530 C. 2 h 50 370 C. 2 h 35 8 Twin rolls 370 C. 2 h 530 C. 2 h 70 370 C. 2 h 35 9 Twin rolls 370 C. 2 h 530 C. 2 h 30 370 C. 2 h 20 10 Twin rolls 370 C. 2 h 530 C. 2 h 30 370 C. 2 h 60 Comparative 11 Twin rolls 270 C. 2 h 530 C. 2 h 30 370 C. 2 h 35 example 12 Twin rolls 470 C. 2 h 530 C. 2 h 30 370 C. 2 h 35 13 Twin rolls 530 C. 2 h 30 370 C. 2 h 35 14 Twin rolls 370 C. 2 h 400 C. 2 h 30 370 C. 2 h 35 15 Twin rolls 370 C. 2 h 600 C. 2 h 30 370 C. 2 h 35 16 Twin rolls 270 C. 2 h 370 C. 2 h 30 370 C. 2 h 35 17 Twin rolls 530 C. 2 h 370 C. 2 h 30 370 C. 2 h 35 18 Twin rolls 370 C. 2 h 30 370 C. 2 h 35 19 Twin rolls 370 C. 2 h 530 C. 2 h 30 370 C. 2 h 10 20 Twin rolls 370 C. 2 h 530 C. 2 h 30 370 C. 2 h 70 21 DC 370 C. 2 h 530 C. 2 h 30 370 C. 2 h 35

[0079] Then, the fin materials thus produced were used as test materials (Test Materials No. 1 to 63), and were subjected to braze-heating. Thereafter, for each of the test materials, evaluations on mechanical strength, electrical conductivity, brazing property, and corrosion resistance were carried out by the methods described below. The results are shown in Tables 3 and 4. Herein, the measurement of electrical conductivity was intended to evaluate the thermal conductivity of the fin materials, and in the case of aluminum alloys, it can be judged that a higher electrical conductivity is associated with a better thermal conductivity. In this specification, braze-heating implies that, unless otherwise specified, the simple substance of any of test material is heated at a temperature for a time period, under the heating conditions that assume the actual brazing of the fin materials.

[a] Density of Second Phase Particles Before Braze-Heating (Particles/mm.sup.2):

[0080] The density of the second phase particles having a circle-equivalent diameter of less than 0.1 m was investigated by making the transmission electron microscopy (TEM) observation of the fin material. The film thickness of the observed area was measured from equal-thickness fringes, and the TEM observation was made only at sites where the film thickness would be 0.1 to 0.3 m. Further, the density of the second phase particles having a circle-equivalent diameter of 0.1 m or more was investigated by making the SEM observation of the fin material cross-section. The density of the second phase particles before braze-heating was determined by subjecting the TEM and SEM photographs to the image analysis.

[0081] The observation was made in three viewing fields for each sample, and the TEM and SEM photographs for each viewing field were subjected to the image analysis, to determine the density of the second phase particles before braze-heating. The indicated density is an average value of the values determined from the three viewing fields for each sample. One viewing field measured 5.5 m4.0 m, and for this one viewing field, TEM observation was made at a magnification ratio of 50,000 times, and SEM observation was made at a magnification ratio of 2,000 times.

[b] Corrugation Forming Property:

[0082] Each of the test materials was slit at a width of 16 mm, a corrugation forming machine was adjusted so as to give a fin ridge height of 5 mm and an interval of fin ridges of 2.5 mm, and the test material was subjected to corrugation forming, to thereby produce a fin with 100 ridges. Then, the fin ridge height was measured, and the case in which there were 10 or more fin ridges having a fin height of 5 mm10% or more due to fluctuation in the fin height, was rated as poor D, or the case in which the average interval of fin ridges was measured, and the average interval of fin ridges was 2.75 mm or more due to springback, was rated as poor D. The cases other than those were rated as good A in terms of corrugation forming property.

[c] Grain Size (GS) Before Braze-Heating (Nn):

[0083] A surface (L-LT face) of each of the test materials was subjected to electrolytic polishing and Barker etching, and then the grain microstructure thereof was observed with an optical microscope. The grain size was measured by a line intercept method of: drawing two diagonal lines on an optical microscopic photograph, and counting the number of grains that are intersected with those lines.

[d] Tensile Strength (TS) after Braze-Heating (N/mm.sup.2):

[0084] Each of the test materials was braze-heated under the conditions of 600 C.3 min, and then cooled at a cooling speed of 50 C./min. Then, the test material was left to stand for one week at room temperature, and this was used as a sample. Then, for each sample, the tensile test was conducted, according to JIS Z2241, at normal temperature, under the conditions of a tensile speed of 10 mm/min and a gauge length of 50 mm.

[e] Electrical Conductivity (EC, % IACS):

[0085] Each of the test materials was braze-heated under the conditions of 600 C.3 min, and then cooled at a cooling speed of 50 C./min, which was used as a sample. For each sample, the electrical conductivity was determined by measuring the electrical resistance, according to JIS H0505, in a thermostat at 20 C. The unit % IACS used in this specification represents the electrical conductivity defined under JIS H0505.

[f] Whether there was Observed Diffusion and/or Melting of the Solder in the Fin, or Not:

[0086] As illustrated in FIG. 1, each of the corrugation-formed test materials (fin 11), and a brazing sheet 12 were provided, respectively, which brazing sheet had a sheet thickness of 0.3 mm, and which brazing sheet had JIS3003 as a core alloy 13 that was clad at 10% cladding ratio on one surface thereof with a filler alloy 14 of JIS4045. Then, the test material 11 and the surface on the filler alloy 14 side of the brazing sheet 12 were superimposed, to form a core 10 for evaluation, as illustrated in FIG. 1, and this core 10 for evaluation was subjected to braze-heating under the conditions of 600 C.3 min. Microscopic observation of a cross-section was conducted for the core 10 for evaluation, and whether there was observed diffusion and/or melting of the solder in the fin, or not, was checked. For the evaluation, the case without any of diffusion and melting of the solder was rated as satisfactory A, and the case with any one or both of diffusion and melting of the solder was rated as poor D.

[g] Evaluation of Self-Corrosion Resistance (Measurement of an Amount of Corrosion Loss (%)):

[0087] Each of the test materials was braze-heated under the conditions of 600 C.3 min, and then cooled at a cooling speed of 50 C./min, which was used as a sample. Then, for each sample, a brine spray test was conducted for 200 hours, according to JIS Z2371, and then the amount of the corrosion loss was measured.

[h] Natural Potential (mV):

[0088] Each of the test materials was braze-heated under the conditions of 600 C.3 min, and then cooled at a cooling speed of 50 C./min, which was used as a sample. Then, for each sample, the natural potential (vs Ag/AgCl) of the fin was measured in a 5% aqueous NaCl solution at 25 C., to evaluate. For the evaluation, when the natural potential was lower than 720 mV, the sample was rated as satisfactory A, and when the natural potential was higher than 720 mV, the sample was rate as poor D.

TABLE-US-00003 TABLE 3 Density of 2nd phase particles before braze-heating Density of Density of GS particles of particles of before Production Sheet Raw Corrugation less than 0.1 m or braze- Alloy process thickness sheet forming 0.1 m more heating Sample No. No. No. (m) TS (TS.sub.B TS.sub.A)/t property (particles/mm.sup.2) (particles/mm.sup.2) (m) Example 1 1 2 60 187 1.08 A 2.3 10.sup.6 1.7 10.sup.5 420 according 2 2 2 60 190 0.92 A 3.3 10.sup.6 1.8 10.sup.5 450 to 3 3 2 60 197 0.83 A 4.5 10.sup.6 2.2 10.sup.5 480 this 4 4 2 60 184 0.65 A 7.2 10.sup.6 8.1 10.sup.4 880 invention 5 5 2 60 208 1.17 A 2.7 10.sup.6 2.8 10.sup.5 430 6 6 2 60 176 0.85 A 2.1 10.sup.6 1.5 10.sup.5 350 7 7 2 60 214 1.13 A 4.1 10.sup.6 1.9 10.sup.5 480 8 8 2 60 188 0.88 A 3.4 10.sup.6 1.8 10.sup.5 460 9 9 2 60 190 0.90 A 3.2 10.sup.6 1.9 10.sup.5 450 10 10 2 60 191 0.93 A 3.2 10.sup.6 1.8 10.sup.5 450 11 11 2 60 194 0.97 A 3.3 10.sup.6 1.8 10.sup.5 440 12 12 2 60 200 1.02 A 3.6 10.sup.6 1.6 10.sup.5 410 13 13 2 60 215 1.22 A 3.7 10.sup.6 2.0 10.sup.5 400 14 14 2 60 192 0.92 A 3.2 10.sup.6 1.8 10.sup.5 420 15 15 2 60 195 0.92 A 3.3 10.sup.6 1.8 10.sup.5 420 16 16 2 60 199 0.92 A 3.5 10.sup.6 1.7 10.sup.5 440 17 17 2 60 190 0.90 A 3.6 10.sup.6 1.5 10.sup.5 600 18 18 2 60 191 0.85 A 3.9 10.sup.6 1.9 10.sup.5 720 19 19 2 60 191 0.82 A 4.3 10.sup.6 1.7 10.sup.5 800 20 20 2 60 192 0.95 A 3.8 10.sup.6 1.8 10.sup.5 520 21 21 2 60 192 0.92 A 4.2 10.sup.6 2.1 10.sup.5 550 22 22 2 60 194 0.85 A 4.3 10.sup.6 2.0 10.sup.5 600 23 23 2 60 192 0.97 A 3.5 10.sup.6 1.9 10.sup.5 440 24 24 2 60 191 0.85 A 3.9 10.sup.6 1.5 10.sup.5 450 25 25 2 60 194 0.80 A 3.9 10.sup.6 1.7 10.sup.5 440 Comparative 26 26 2 60 182 1.07 A 1.2 10.sup.6 1.7 10.sup.5 400 example 27 27 2 60 204 0.88 A 6.2 10.sup.6 2.4 10.sup.5 490 28 28 2 60 185 0.63 D 8.7 10.sup.6 6.7 10.sup.4 1,150 29 29 2 60 215 1.23 A 2.2 10.sup.6 3.2 10.sup.5 480 30 30 2 60 175 0.93 A 1.7 10.sup.6 1.4 10.sup.5 360 31 31 2 60 227 1.30 A 4.7 10.sup.6 2.2 10.sup.5 510 32 32 2 60 191 0.92 A 3.5 10.sup.6 1.9 10.sup.5 460 33 33 2 60 190 0.90 A 3.3 10.sup.6 1.9 10.sup.5 450 34 34 2 60 224 1.32 A 3.5 10.sup.6 1.8 10.sup.5 400 35 35 2 60 208 1.07 A 3.5 10.sup.6 2.0 10.sup.5 420 36 36 2 60 197 0.90 D 4.3 10.sup.6 1.8 10.sup.5 1,030 37 37 2 60 198 0.90 A 4.1 10.sup.6 2.0 10.sup.5 660 38 38 2 60 200 0.88 A 4.0 10.sup.6 1.9 10.sup.5 460 Properties after braze-heating Whether there was observed Amount of Production diffusion and/or corrosion Natural Alloy process TS EC melting of the loss potential Sample No. No. No. (N/mm.sup.2) (% IACS) solder, or not (%) (mV) Remarks Example 1 1 2 122 42 A 3.2 A according 2 2 2 135 44 A 3.3 A to 3 3 2 147 44 A 3.5 A this 4 4 2 145 43 A 2.9 A invention 5 5 2 138 45 A 3.9 A 6 6 2 125 45 A 3.4 A 7 7 2 146 41 A 3.3 A 8 8 2 135 44 A 3.1 A 9 9 2 136 44 A 3.3 A 10 10 2 135 44 A 3.8 A 11 11 2 136 44 A 3.3 A 12 12 2 139 42 A 3.7 A 13 13 2 142 41 A 3.8 A 14 14 2 137 44 A 3.4 A 15 15 2 140 42 A 3.4 A 16 16 2 144 40 A 3.5 A 17 17 2 136 44 A 3.4 A 18 18 2 140 43 A 3.4 A 19 19 2 142 41 A 3.4 A 20 20 2 135 44 A 3.3 A 21 21 2 137 42 A 3.4 A 22 22 2 143 40 A 3.4 A 23 23 2 134 44 A 3.1 A 24 24 2 140 42 A 3.3 A 25 25 2 146 39 A 3.3 A Comparative 26 26 2 118 41 A 2.9 A example 27 27 2 151 43 D 3.8 A 28 28 2 147 42 D 2.5 A 29 29 2 141 44 A 3.7 A GC occurred 30 30 2 119 46 D 3.6 A 31 31 2 149 42 A 3.4 A GC occurred 32 32 2 136 44 A 3.1 D 33 33 2 136 43 A 4.2 A 34 34 2 145 39 A 4.1 D 35 35 2 144 38 A 3.5 A GC occurred 36 36 2 143 39 A 3.5 A GC occurred 37 37 2 144 39 A 3.4 A GC occurred 38 38 2 147 38 A 3.2 A GC occurred (Note) GC occurred: Giant intermetallic compounds (GC) were occurred upon casting.

TABLE-US-00004 TABLE 4 Density of 2nd phase particles before braze-heating Density of Density of GS particles of particles of before Production Sheet Raw Corrugation less than 0.1 m or braze- Alloy process thickness sheet forming 0.1 m more heating Sample No. No. No. (m) TS (TS.sub.B TS.sub.A)/t property (particles/mm.sup.2) (particles/mm.sup.2) (m) Example 39 1 1 40 194 1.85 A 1.5 10.sup.6 6.2 10.sup.4 420 according 40 1 2 40 184 1.55 A 2.3 10.sup.6 1.7 10.sup.5 430 to this 41 1 3 40 181 1.50 A 1.2 10.sup.6 7.3 10.sup.4 400 invention 42 1 4 40 196 1.80 A 3.5 10.sup.6 1.8 10.sup.5 520 43 1 5 40 174 1.33 A 7.8 10.sup.5 5.5 10.sup.4 340 44 1 6 40 184 1.58 A 1.2 10.sup.6 2.0 10.sup.5 400 45 1 7 40 190 1.68 A 2.5 10.sup.6 1.5 10.sup.5 440 46 1 8 40 202 1.98 A 2.3 10.sup.6 1.4 10.sup.5 440 47 1 9 40 175 1.35 A 2.3 10.sup.6 1.7 10.sup.5 460 48 1 10 40 207 2.03 A 2.4 10.sup.6 1.8 10.sup.5 430 49 1 2 50 185 1.26 A 2.3 10.sup.6 1.7 10.sup.5 440 50 1 2 80 188 0.81 A 2.3 10.sup.6 1.7 10.sup.5 420 51 1 2 150 188 0.43 A 2.3 10.sup.6 1.7 10.sup.5 440 Comparative 52 1 11 40 187 1.73 A 1.2 10.sup.6 3.8 10.sup.4 400 example 53 1 12 40 177 1.50 A 8.9 10.sup.5 3.3 10.sup.4 320 54 1 13 40 186 1.70 A 7.7 10.sup.5 4.2 10.sup.4 440 55 1 14 40 225 2.48 D 3.5 10.sup.7 5.4 10.sup.4 Fiber* 56 1 15 40 180 1.63 A 5.4 10.sup.5 3.9 10.sup.4 330 57 1 16 40 238 2.83 D 6.8 10.sup.7 2.8 10.sup.4 Fiber* 58 1 17 40 181 1.60 A 6.9 10.sup.5 3.8 10.sup.4 420 59 1 18 40 229 2.53 D 6.5 10.sup.7 2.8 10.sup.4 Fiber* 60 1 19 40 168 1.08 A 2.4 10.sup.6 1.8 10.sup.5 450 61 1 20 40 216 2.23 D 2.3 10.sup.6 1.7 10.sup.5 420 62 1 21 40 167 1.35 A 7.7 10.sup.5 1.2 10.sup.4 120 63 1 19 150 170 0.29 A 2.5 10.sup.6 1.8 10.sup.5 420 Properties after braze-heating Whether there was observed Amount of Production diffusion and/or corrosion Natural Alloy process TS EC melting of the loss potential Sample No. No. No. (N/mm.sup.2) (% IACS) solder, or not (%) (mV) Remarks Example 39 1 1 120 41 A 3.2 A according 40 1 2 122 42 A 3.2 A to this 41 1 3 121 42 A 3.4 A invention 42 1 4 124 42 A 3.2 A 43 1 5 121 43 A 3.3 A 44 1 6 121 42 A 3.3 A 45 1 7 123 42 A 3.1 A 46 1 8 123 42 A 3.2 A 47 1 9 121 42 A 3.5 A 48 1 10 126 42 A 3.2 A 49 1 2 122 42 A 3.3 A 50 1 2 123 42 A 3.1 A 51 1 2 124 42 A 2.9 A Comparative 52 1 11 118 41 A 3.3 A example 53 1 12 117 42 A 3.3 A 54 1 13 118 42 A 3.2 A 55 1 14 126 41 A 3.1 A 56 1 15 115 43 A 3.2 A 57 1 16 125 42 A 3.3 A 58 1 17 117 42 A 3.2 A 59 1 18 128 42 A 3.3 A 60 1 19 125 42 D 3.2 A 61 1 20 127 42 D 3.3 A 62 1 21 113 39 D 3.3 A 63 1 19 127 42 D 3.0 A (Note) Fiber*: Fiber microstructure was remained.

[0089] As is apparent from the above results, the followings can be understood.

[0090] In Test Materials Nos. 28, 36, 55, 57, 59, 61, and 63, as the tensile strength before braze-heating was high, this resulted in that fins did not shrink to a predetermined distance at the time of corrugation forming, the height of the fins (the fin ridge height) fluctuated due to the fact that the grains before braze-heating were larger than a predetermined size, or because the relationship of formula 1 was not satisfied, corrugation formability was poorer to that in the Examples according to the present invention.

[0091] In Test Materials Nos. 26, 30, 52, 53, 54, 56, 58, and 62, the tensile strength after braze-heating was low, which was not sufficient.

[0092] Test Material No. 27 had a too large content of Si, and thus the melting point of the fin material was lowered, to cause melting of the solder. Test Material No. 28 had a too small content of Fe, and thus the recrystallization temperature was raised, to cause diffusion of the solder without having recrystallization completed at the time of brazing. In Test Material No. 30, since a content of Mn was too small, the amount of solid solution of Si was increased, and the melting point of the fin material was lowered, to cause melting of the solder. In Test Materials Nos. 60 and 63, the final cold-rolling reduction ratio at the time of producing the fin material was too low, and the recrystallization temperature was raised. Thus, diffusion of the solder occurred without having recrystallization completed at the time of brazing. In Test Material No. 61, since the final cold-rolling reduction ratio at the time of producing the fin material was too high, the recrystallized grains became very fine at the time of brazing, and the grain boundaries were eroded by the solder, to cause diffusion of the solder. In Test Material No. 62, since casting at the time of producing the fin material was carried out by a DC method, the recrystallized grains became very fine at the time of brazing, and the grain boundaries were eroded by the solder, to cause diffusion of the solder. As described above, each of those test materials exhibited results with poop in the brazing property, compared to that in the Examples according to the present invention.

[0093] In Test Material Nos. 33 and 34, since the Zn content or the Cu content was too large, the corrosion speed was fast, and the amount of corrosion loss was made large.

[0094] In Test Material No. 32, since the Zn content was too small, the natural potential of the fin could not be lowered sufficiently.

[0095] In Test Materials Nos. 29, 31, and 35 to 38, since the contents of Fe, Mn, Ti, Zr, Cr, and/or V were too large, huge intermetallic compounds were occurred at the time of casting.

[0096] Contrary to the above, Test Materials Nos. 1 to 25 and 39 to 51 of the Examples according to the present invention, each was excellent in the characteristics. That is, the grain size before braze-heating was 1,000 m or less, the corrugation forming property was satisfactory, and the mechanical strength after braze-heating was as high as 120 N/mm.sup.2 or more. Further, no solder diffusion or melting of the solder in the fin occurred, to be good in the brazing property, and the amount of corrosion loss was less than 4.0%. Further, the natural potential was lower than 720 mV, thereby for resulting to show the sacrificial anode effect secured.

[0097] Having described our invention as related to the present embodiments, it is our intention that the invention not be limited by any of the details of the description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

REFERENCE SIGNS LIST

[0098] 10 Core for evaluation [0099] 11 Fin material [0100] 12 Brazing sheet [0101] 13 Core alloy [0102] 14 Filler alloy